The present invention relates to a communication system having a function of measuring the duration of disconnection period of a line.
A key telephone system that accommodates a two-wire type standard telephone holds data for discriminating a hooking operation for requesting to hold a line from a hooking (on-hook operation) for disconnecting the line when a call is completed. When an operator of the standard telephone requests holding, he or she goes on-hook for a short period of time in consideration of a value set as this data. Alternatively, the operator presses a switch or button during a conversation, which is arranged on the standard telephone and is used for setting the telephone an on-hook state for a predetermined period of time, thus outputting a hooking signal.
In a case where a call is disconnected so often due to an on-hook period which is too long when the operator performs the hooking operation during a telephone conversation, or when duration of the hooking signal output by depressing the button and the like is always longer than the set value, a person who is in charge of maintenance of the key telephone system updates data for the set value.
However, in the key telephone system, in order to check whether or not the set value is adequate, it is required to make a telephone call to an outside line or to another terminal via an extension line, by using the standard telephone. If a conversation is still interrupted, after the set value is updated, the person in maintenance must update the value using a master telephone, a maintenance console, or the like, and make a telephone call again using the standard telephone. This operation for updating the set value must be repeated until a call is no longer interrupted by the hooking operation during a conversation.
There is another problem associated with the above-mentioned operation for confirming adequacy of the set value. Since this kind of operation is troublesome, the value tends to be set relatively long so that a call is not readily disconnected. In such case, when a user completes the call to a given person and tries to make another call to another person, the on-hook operation that was intended to disconnect the line may be erroneously determined as a hooking operation for holding the line, and the user may be confused.